1. Field of the Invention
This invention relates to polyarylene-thioether fibers having certain physical properties of exceptionally excellent (high) values (herein referred to as high-quality fibers) and a method for continuously producing these fibers. More particularly, it relates to high-quality fibers having properties which heretofore have not been mutually compatible and consisting essentially of a linear polyarylene-thioether having a melt viscosity of 5,300 to 20,000 poise (at 310.degree. C. and a shear velocity of 200 second.sup.-1) and relates well to a method for continuously producing these high-quality fibers without breaking and fluffing.
2. Prior Art
It has been expected that a polyarylene-thioether, and especially polyphenylene-thioether, can be processed into heat-resistant fibers having excellent properties, because they are highly crystalline thermoplastic polymers having thermal resistance. For example, methods for producing such fibers are disclosed in Japanese Patent Publication No. 30609/1977 and, Japanese Laid-open Patent Application Nos. 143518/1982 and 31112/1983.
These methods, however, use as starting materials a polymer having a relatively low melt viscosity, a nonlinear polymer produced by high-temperature curing, or a non-linear polymer produced with a crosslinking agent in the course of polymerization. The unsatisfactory properties of fibers and the like observed in the case of a polymer having low melt viscosity may have been solved by the use of the latter non-linear polymer. Such nonlinear polymers, however, have poor spinnability and stretchability and suffer from breaking and fluffing in the course of continuous melt spinning and continuous stretching. Thus, it has been very difficult to industrially produce stretched filaments.
On the other hand, a linear polymer which is not crosslinked with the high-temperature crosslinking or crosslinking polymerization has lacked satisfactorily high melt viscosity. Such linear polymers have excellent spinnability and stretchability but have unsatisfactory fiber properties, have bad melt-breaking resistance, and suffer from melt breaking and fluffing in the course of continuous melt spinning and subsequent continuous heat setting. Thus, it has been also difficult to industrially produce stretched heat-set fibers and to obtain fibers having excellent mechanical properties and thermal resistance.